more on breathers

[A_HRD]

Just to be clear,

The Mac Read breather uses a Non Return Valve on the timing chest and a condensation system which returns oil down a capillary tube to the D Cap - exactly as explained by Ian (b'knighted) above. I have had one on my Rapide for about 30 years. Yes, it is pig-ugly but still works perfectly to this day holding a partial vacuum in the crankcases - so no leaks. I fit a plastic "compressor silencer" to a piece of rubber tube at the outlet end - hidden under the tank. This removes the plop-plop sound of the NRV. I like my Vincents to be shiny - but also practical and trouble-free to use over long distances. This fits the bill perfectly. If I want to go back to standard for any reason; it takes 10 minutes.

The R Kemp breather takes a slightly different tack using the slow movement of oil-laden air through a large volume of "wire wool" to condense oil back in the timing case. I have never used this system but know plenty of people who have and they have been pleased with its function.

I'll try and add an old photo or two of the Rap…

Peter B
Bristol, UK.

 

[clevtrev]

Trever uses a reed valve.

Sorry, never ever used anything other than standard, but then I did have round bores, that stayed that way through the whole temperature range.

 

[A_HRD]

 

[clevtrev]

Hi Useful',

You are nearly there, but if it were perfect, what would you have to talk about?

There has been so much talked and written about breathers since the bikes were in production that the solution is definitely out there, and is probably on this forum.
First I'd recommend searching past threads for a variety of opinions. You may find you need to answer some questions, like what size breather pipe do you use and a how long is it? - the idea being that perhaps it's volume has to be able to cope with the engine displacement without pumping out of the end. I think that was why Know Thy Beast suggests pipes to behind the pillion footrest.

My own thought is that the breather developed decades ago by Mac Read is the cure for all problems. It is disliked by some as it adds an external pipe, the so called elephants trunk, vertically from the ATD cover. This has a shuttle valve (PCV?) close to the cover and the blown gas goes to separator chamber which has a capilliary tube for oil to be sucked back into the D breather cap. The exhaust from this separator is a short oil free pipe. This is used with the timed breather outlet blanked.
There are other breathers also called elephant trunks which aimed to copy Mac Read's but not all were successful.

The so called Mac Read valve, was originally thought out by Ivan Caffrey of the York section. Credit where it`s due, likewise the Dave Hills stand was the creation of Larry Honour of Liphook.

 

[vibrac]

I am happy that the beather I use on the racers is just 2-3 inches long and same diameter as the breather pipe I dont think a large device would go down well with the "look standard" tribe

 

[Kansas Bad Man]

Must have misunderstood your post Trever, cant understand, we even talked about the material of your reed compared to mine.

 

[Vince Farrell]

Sorry Trevor, I was around at the time and knew Ivan well. He didn't start making them 'till Mac said he wasn't making any more. Ivan's version (I still have two of them) used a large bore stainless tube instead of rubber. The sound of the ball valve drove me spare so I took them out, stopped the noise but introduced condensation. This was also true of the Kemp trunk, cured oil escaping but at a price.

Vince Farrell

 

[paulpackman]

I cracked this one years ago.
The crankcase volume changes by nearly one litre at every rev as both pistons go up and down almost together and so breathing is a problem
especially when you add to it blow by past the pistons. Any atmospheric breather must be of low inertia (no ball valves) so that it is sensitive
to the pulses of the engine up to 6000 rpm or so.
Firstly your bike should have good bores and rings otherwise you will be wasting your time.
I have blanked off the timed breather and fitted a Kevlar disc valve (low inertia) on the top cap of the front exhaust valve of my twin
which is very obscure, out of the way and does not spoil the look of the bike.
I drilled holes in the underside (non stressed part) of the exhaust rocker housing and ported past the upper valve guide giving a
vent of about half an inch square. The valve housing is the full diameter of the top cap and has eight quarter inch holes in it over
which a Kevlar disc is attached. I have blanked off the oil feed to the front rocker as enough oil mist gets up there from the engine
which drops out in the large diameter valve cap from which a half inch pipe leads to the back of the bike.
All I get from the end of the breather pipe is a little moisture from the products of combustion.
QED

 

[Simon Dinsdale]

Hi Paul

Very interesting your reply about breathers. I have played with this problem for several year having not liked the look of the elephant breather. Do you have any more details or photos of this Kevlar disc valve. Did you purchase the working parts or manufacture them? I remember discussing it with you at Fordingbridge annual rally and would be interested in any details wIth a view to potentially replicate what you have for myself.

Cheers
Simon

 

[vibrac]

I cracked this one years ago.
The crankcase volume changes by nearly one litre at every rev as both pistons go up and down almost together and so breathing is a problem

I thought this was disproved a few years ago by the French letter test? I certainly found with my PCV valve that on starting the 'bag' inflated to a few 1000 cc and then stabilized since the crankcase is now below atmospheric and the valve is preventing the air return